As is well known in the art, electro-winning refers to the technique of extracting a metal from its soluble salt by an electrolytic cell. It is used in recovery of zinc, cobalt, chromium, and manganese, and has recently been applied to copper when in the form of a silicate ore. For any specific metal, the salt in solution is subjected to electrolysis and is electro-deposited on a cathode starter plate. In particular, electro-winning techniques used to produce pure metallic copper from leach/solvent electrolytes consist of applying an electrical potential between inert lead alloy anodes and stainless steel or copper cathodes immersed in a CuSO4—H2SO4—H2O electrolyte. Copper metal is deposited at the cathode and oxygen gas released at the anode. Purity of the refined copper can be maximized by, amongst other factors, providing for straight cathodes fabricated from stainless steel arranged vertically in the electrolytic bath and positioned at uniform distances.
Similarly, electro-refining refers to a technique for purifying metals by electrolysis using an impure metal as anode from which the pure metal is dissolved and subsequently deposited at the cathode. In particular, when electro-refining copper, copper is dissolved from impure copper anodes into a CuSO4—H2SO4—H2O electrolyte. Pure copper without the anode impurities is plated onto the cathodes. Copper refined in this manner is of very high purity, typically with less than 20 ppm impurities plus oxygen which is controlled at about 0.025%.
When another metal, such as stainless steel, is used to fabricate the starter plate the refined metal deposited on the starter plate must be subsequently removed. In order to strip a starter plate covered with refined metal the prior art reveals systems where the plate is moved between a number of stations for washing, stripping, refinishing, etc. One problem with moving the plate is the weight of the deposited metal, which can be in excess of 300 kg., thereby requiring a robust and rugged structure for moving the plates.
Prior art systems include those using a linear conveyer, wherein the cathodes are conveyed, supported on a bottom edge, by a narrow pan-type conveyor, through multiple stripping stations. Other prior art systems, such as the one taught in U.S. Pat. No. 5,149,410 include those based on a rotary, top driven carousel with cathode plates conveyed through multiple stripping stations by the carousel. The cathode plates are suspended by hanger bars from supports mounted to the carousel base. One drawback of these systems is that, once separated from the starter plates, the metal deposit plates drop at least their full length to be removed by a conveyor. Additionally, the high mass with great inertia of the structure requires a heavy duty drive unit with its associated high capital cost.
There thus remains a need for an improved method and apparatus to stripping electro-deposited sheets from permanent cathodes.